这是我写的C用的DateAdd函数。

SYSTEMTIME cDateAdd(SYSTEMTIME SourceDate,DWORD SecondNumber)
{
SYSTEMTIME st;
time_t timer;
struct tm *ptm;

ptm=malloc( sizeof(struct tm) );

ptm->tm_year=SourceDate.wYear-1900;
ptm->tm_mon=SourceDate.wMonth-1;
ptm->tm_mday=SourceDate.wDay;
ptm->tm_hour=SourceDate.wHour;
ptm->tm_min=SourceDate.wMinute;
ptm->tm_sec=SourceDate.wSecond;

timer=mktime(ptm);
timer=timer+SecondNumber;
ptm=localtime(&timer);

st.wYear=ptm->tm_year+1900;
st.wMonth=ptm->tm_mon+1;
st.wDay=ptm->tm_mday;
st.wHour=ptm->tm_hour;
st.wMinute=ptm->tm_min;
st.wSecond=ptm->tm_sec;

return st;
}